In recent years, wireless power supply systems have received increased attention because of some of their benefits over traditional wired power supply systems. Some more basic wireless power supply systems are specifically designed to charge a particular device, which can help minimize power transfer efficiency issues. Other wireless power supply systems attempt to account for misalignment, charge different remote devices and provide different amounts of power. In these systems, maintaining an acceptable power transfer efficiency can be difficult.
Some wireless power systems adjust the operating frequency of an AC signal across the tank circuit closer to or further from resonance to increase or decrease the amount of power delivered to the remote device. Other wireless power systems adjust the resonant frequency of the tank circuit closer to or further from the operating frequency. One issue with these systems is that the power transfer efficiency between the inductive power supply and the remote device is a function of how close the operating frequency is to resonance. So, while adjusting the operating frequency or resonant frequency can provide some control over the amount of power delivered to the remote device, it may come at the cost of decreased power transfer efficiency.
Other wireless power supplies use a fixed operating frequency and instead adjust the rail voltage, duty cycle, or phase of the AC signal across the tank circuit to increase or decrease the amount of power delivered to the remote device. One issue with this is that in order for the power transfer efficiency to be acceptable, the inductive power supply and remote device may need to be precisely aligned and specifically designed to work with each other.